Determination of the Combustion Behaviour of 2nd Generation Biomass Fuels

In order to determine the combustion behaviour of 2nd generation biomass fuels test runs were performed at BIOENERGY 2020+ within the EU-project BRISK. Pellets from the Hydrothermal Carbonisation (HTC) process (HTC coal pellets) and vineyard pruning pellets were used as fuels for the investigation. The combustion behaviour of these fuels was determined during test runs at a pilot-scale combustion plant. The overall aim of the test runs was the determination of appropriate operating conditions, to optimise combustion parameters in order to minimise particulate matter and gaseous emissions as well as to avoid ash related problems. During the test runs it was clearly indicated that especially flue gas recirculation below the grate plays a major role in the thermochemical conversion of new biomass fuels with higher ash contents compared to woody biomass. It ensures moderate temperatures in the fuel bed, avoids ash related problems (slagging) on the grate and leads to stable operation conditions with reduced gaseous and particulate matter (PM) emissions. Furthermore, a reduced gas velocity in the fuel bed results in reduced entrainment of ash from the grate and hereby reduces the PM emissions. Therefore, and in order to achieve a good burnout quality of the fuel, an increased residence time on the grate is recommended, which can be realised by an adapted grate concept. In conclusion, the optimisation of operation parameters by primary measures showed a big potential for a stable plant operation combined with reduced emissions. Thus provides the basis for the required further development of combustion systems for these 2nd generation biomass fuels.